The long-term objective of this research is to provide a clearer understanding of the role the hippocampal region plays in memory function. This is a particularly important health related issue because this region of the brain is critically important for memory, yet is vulnerable to damage in various pathological conditions, including those associated with stroke, aging, and Alzheimer's disease. We propose to examine the effects of specific lesions restricted to the hippocampal region on performance on the delayed nonmatching to sample (DNMS) task and the delayed recognition span task (DRST). The specific aims related to this study are: 1) to determine whether the hippocampal region has a special role in spatial memory and 2) to determine whether damage limited to the hippocampal region that includes damage to white matter fibers produces the same effects as damage limited to the hippocampus that spares white matter fibers. These aims will be accomplished by preparing two groups of monkeys with bilateral lesions limited to the hippocampal region that spare the cortical components of the medial temporal lobe memory system (the entorhinal, perirhinal, and parahippocampal cortices). One group will receive radiofrequency lesions and the other group will receive ibotenate lesions. The two groups of operated monkeys and one group of normal control monkeys will be tested on spatial and nonspatial versions of the DNMS and DRST tasks to determine whether the hippocampal region plays a disproportionate role in spatial memory and whether the behavioral effects of lesions of the hippocampal region are dependent on damage to the white matter fibers in the region.